The present invention relates to polymer-ceramic composite interconnection substrates for high performance electronic and optical packaging solutions. The present invention is particularly concerned with highly thermally conductive and electrically insulating substrates with improved chip-to-substrate and substrate-to-card interconnection reliability by employing ceramic-filled polymers and polymer-filled ceramics for the packaging substrate with low dielectric constant and a coefficient of thermal expansion (CTE) close to that of the silicon device and the substrate or the substrate and the printed circuit board.
Multilayered interconnection substrates are used for the packaging or mounting of semiconductor devices. The substrate may comprise patterned metal layers which act as electrical conductors sandwiched between dielectric layers which act as electrical insulators. The substrates may be designed with termination pads for attaching, in addition to semiconductor devices, connector leads, capacitors, resistors, covers, etc. Interconnection between buried conductor levels can be achieved through metal-filled vias. The substrates can be made from a variety of ceramic and polymeric materials.
Multilayer interconnection packaging substrates where ceramic substrates with high density semiconductor devices are connected to a printed circuit board (PCB) with pins or solder bumps have the problem of thermal mismatch between contacting materials due to a significant difference in the coefficient of thermal expansion (CTE) between the ceramic chip carrier or the substrate and the PCB materials which impacts the second level joining reliability. Moreover, such ceramic substrates generally have high fabrication cost.
The printed circuit board materials are typically comprised of glass filled epoxy, typically FR-4 fire-retardant epoxy-glass laminates or prepregs, polyimide-glass, BT/Epoxy (bis-maleimide-triazine resins), and cyanate ester resin impregnated glass cloth. Other PCB base materials having higher glass transition temperature (Tg) and lower CTE that have been made available for improved thermal and electrical properties over conventional epoxy based circuit board materials include reinforced thermoplastics, typically, fiber reinforced polyester, glass microspheres filled polyester; PPO [poly(phenylene oxide)] and epoxy resin blends such as GETEK laminates and prepregs, polyimide-glass filler composite materials comprising polyester-imide, amide-imide-ester, or amide-imide as the matrix resin. For low dielectric constant polymer-filler composites, fluoropolymer based laminating materials typically derived from perfluoroalkylene such as poly(tetrafluoroethylene)(PTFE), copolymers of tetrafluoroethylene and hexafluoropropylene, and related materials have been extensively investigated. Fluoropolymers reinforced with fiber glass particulate are commercially available such as those from Rogers corporation under the trade name designation RO2800, RO2500, and related compositions. Fluoropolymer based composite materials are characterized by low dielectric constant, however, these materials have the problem of poor dimensional stability, low glass transition temperature (Tg), high CTE, poor adhesion to metals which requires elaborate bonding schemes, and have high thermal flow which causes heat induced via deformation in processes where laser etching is used for via formation. Also, the fluorocarbon polymer-based composite matrix is not compatible with photoimaging, an imaging option available with epoxies and polyimide based insulating materials. Some of these materials also suffer from poor thermal stability (i.e., they start degrading when heated to temperatures above about 250xc2x0 C.).
The prior art is replete with those who have made efforts to make and improve the properties of composite substrates consisting of polymeric and ceramic materials.
U.S. Pat. No. 5,061,548 (Arthur et al.), the disclosure of which is incorporated by reference herein, describes a ceramic filled fluoropolymer composite material where the ceramic filler is precoated with a silane coupling agent, where the composite material is thermally flowable and is used as a bond-ply in a multilayer circuit board. U.S. Pat. No. 5,287,619 (Smith et.al.), the disclosure of which is incorporated by reference herein, describes a silane-coated silica filled fluoropolymer (PTFE) composite and its use in the fabrication of high density interconnect devices as multilayer MCM substrates by an additive process using multiple layers of copper and thermoplastic fluoropolymer composite dielectric. Solid Cu vias are used for interconnection between layers of MCM substrates or to semiconductor devices to be packaged in the module. U.S. Pat. No. 5,384,181 (Arthur et.al.), the disclosure of which is incorporated by reference herein, describes a silane-coated fused amorphous silica filled fluoropolymer composite where the silane coating material is a blend of phenyl silane and fluorosilane. These patents relate to fluoropolymers which have poor adhesion to metals, low glass transition temperature and high CTE (e.g., 70 ppm/xc2x0C. as disclosed in Arthur et al.)
U.S. Pat. No. 5,358,775 (A. F. Horn), the disclosure of which is incorporated by reference herein, is concerned with a high dielectric constant (k greater than 4) and relatively high CTE ( less than 35 ppm/xc2x0C.) electrical substrate material for microwave applications comprising a fluoropolymer filled with ceramic particles that exhibits low dielectric loss, high dielectric constant (Kxe2x80x2 greater than 4), and high thermal coefficient of dielectric constant (TCKxe2x80x2) for capacitors.
U.S. Pat. No. 5,541,249 (Hughes et.al.), the disclosure of which is incorporated by reference herein, discloses injection moldable polymer-filler composite compositions comprising organo-silicone polymer treated inorganic or metallic fillers in organic matrix resins including polyolefins, polyimides, polycarbonate, and polyacetals. Various inorganic fillers used include silicon nitride, carbide, alumina, aluminum nitride, titania, zirconia, and mixtures thereof, and the metals include iron, stainless steel, chromium alloy, nickel alloy and bronze. This patent merely discusses the materials and makes no mention of the applications of the material or their physical properties such as CTE and dielectric constant.
U.S. Pat. No. 5,571,609 (M. E. St. Lawrence el. al.), the disclosure of which is incorporated by reference herein, discloses a substrate material comprising a thermosetting matrix of polybutadiene and polyisoprene containing butadiene and isoprene, woven glass fabric, ceramic filler, fire retardant, and peroxide cure initiator. The composite material is claimed to have lower CTE in the z-direction and improved electrical performance. This class of materials, however, is unsatisfactory due to poor tear resistance, low Tg, low thermal stability, long cure times, high thermal expansion, low upper use temperature, poor solvent resistance, and susceptibility to photooxidation.
U.S. Pat. No. 4,810,563 (DeGree et al.), the disclosure of which is incorporated by reference herein, discloses a multilayer substrate article including top and bottom metal layers and insulating layers of ceramic-filled polyamide-polyimide matrix resin. The polyamide-polyimide layers are adhered to one another with an epoxy bonding layer. The disclosed article has the limitations of significant moisture absorption due to the poly(amide-imide) matrix, epoxy adhesive layer performance limitation in terms of its low thermal stability, low Tg which coupled with relatively high dielectric constant of the composite results in marginal properties of the entire package.
In plastic packaging structures, the integrated circuit (IC) devices are connected to an organic substrate fabricated using curable compositions containing a thermosetting binder such as polyepoxides, cyanate ester/epoxy resin blends with inorganic filler reinforcement. Thermoplastic composite dielectric materials having low dielectric constant, such as the particulate filled fluoropolymer composite laminates have been marketed by Roger Corp. for interconnection structures. Other low dielectric constant laminating materials that have been described for organic substrates structures are fabricated by impregnation of fluoropolymer laminates with thermosetting resins, typically cyanate ester resins.
Accordingly, it is a purpose of the present invention to have an organic-inorganic composite electronic substrate which is economical to manufacture.
It is another purpose of the present invention to have a composite electronic substrate which has a low dielectric constant, low impedance, low CTE, low birefringence, high package-to-card reliability, and low stress component interconnection stress.
It is yet another purpose of the present invention to have a composite electronic substrate which has a high Tg and good thermal stability.
It is also the purpose of this invention to have a composite electronic substrate which has a low moisture absorption.
These and other purposes of the present invention will become more apparent after referring to the following description of the invention.
The purposes of the invention have been obtained by providing according to a first aspect of the invention a composite electronic and/or optical substrate comprising a plurality of adjacent layers, each of the adjacent layers comprising a mixture of a polymeric and a ceramic material, wherein the substrate has a coefficient of thermal expansion of 8 to 14 ppm/xc2x0C. at 100xc2x0 C. and a dielectric constant less than 4.
According to a second aspect of the invention, there is provided a composite electronic and/or optical substrate comprising a plurality of layers, each of the layers comprising a polymer-filled ceramic material wherein the substrate has a coefficient of thermal expansion of 8 to 14 ppm/xc2x0C. at 100xc2x0 C. and a dielectric constant less than 4.
According to a third aspect of the invention, there is provided a composite electronic or optical substrate comprising a plurality of adjacent layers, each of the adjacent layers comprising a ceramic-filled polymeric material having 30 to 90 weight % polymeric material and 10 to 70 weight % ceramic material, wherein the substrate has a coefficient of thermal expansion of 8 to 14 ppm/xc2x0C. at 100xc2x0 C. and a dielectric constant less than 4.
According to a fourth aspect of the invention, there is provided a method of making a composite electronic and/or optical substrate, the method comprising the steps of:
forming a dispersion of polymeric and ceramic materials;
forming a plurality of composite green sheets with the dispersion;
forming via holes in each of the green sheets;
filling a metal conductor in the via holes of each of the green sheets;
forming a metal conductor on a surface of each of the composite green sheets; and
stacking and laminating the plurality of green sheets to form a composite electronic substrate of adjacent composite layers that has a coefficient of thermal expansion of 8 to 14 ppm/xc2x0C. at 100xc2x0 C. and a dielectric constant less than 4.
According to a fifth aspect of the invention, there is provided a method of making a composite electronic or optical substrate, the method comprising the steps of:
forming a dispersion of polymeric and ceramic materials;
forming a plurality of green sheets with the dispersion;
forming via holes in each of the green sheets;
filling a metal conductor in the via holes of each of the green sheets;
forming a metal conductor on a surface of each of the green sheets;
stacking and laminating the plurality of green sheets to form a composite electronic substrate laminate;
heating the composite electronic substrate to thermally remove the polymeric material and any carbonaceous residue;
partially densifying the ceramic material to produce a rigid skeletal structure;
at least partially filling the rigid skeletal structure with a polymeric material to produce a composite electronic substrate that has a coefficient of thermal expansion of 8 to 14 ppm/xc2x0C. and a dielectric constant less than 4.